Nonaqueous electrolyte secondary battery

ABSTRACT

Provided is a nonaqueous electrolyte secondary battery including a bottomed cylindrical positive electrode casing, and a negative electrode casing which is fixed to an opening of the positive electrode casing through a gasket. The opening of the positive electrode casing is caulked to the negative electrode casing side to seal an accommodation space. A caulking tip end in the opening of the positive electrode casing is disposed in an inward direction of the negative electrode casing than a tip end of the negative electrode casing. A diameter d of the nonaqueous electrolyte secondary battery is in a range of 6.6 mm to 7.0 mm, a height h1 of the nonaqueous electrolyte secondary battery is in a range of 1.9 mm to 2.3 mm, a side surface portion of the positive electrode casing is formed in a curved surface shape, a radius of curvature R is set in a range of 0.8 mm to 1.1 mm, and a height h2 of the positive electrode casing is in a range of 65% to 73% with respect to the height h1 of the nonaqueous electrolyte secondary battery.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to JapanesePatent Application No. 2015-049562 filed on Mar. 12, 2015, the entirecontent of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a nonaqueous electrolyte secondarybattery.

Background Art

The nonaqueous electrolyte secondary battery has been used in a powersupply unit of an electronic apparatus, an electric power storage unitthat absorbs a variation in electric power generation of a powergenerator, and the like. Particularly, a small-sized nonaqueouselectrolyte secondary battery such as a coin-type (button-type) battery,has been widely employed in portable devices as a power supply for motordriving and the like, in addition to a backup power supply as atimepiece function, a backup power supply of a semiconductor memory, anauxiliary power supply of an electronic device such as a microcomputerand an IC memory, and a battery of a solar timepiece (for example, referto JP-A-2000-243449). The coin-type nonaqueous electrolyte secondarybattery employs, for example, a structure in which a positive electrode,a negative electrode, and an electrolyte are accommodated in anaccommodation space surrounded by a bottomed cylindrical positiveelectrode casing and a negative electrode casing, and the positiveelectrode is electrically connected to the positive electrode casing,and the negative electrode is electrically connected to the negativeelectrode casing. In addition, a gasket is interposed between thepositive electrode casing and the negative electrode casing, and thespace between the positive electrode casing and the negative electrodecasing are caulked to seal the accommodation space of the nonaqueouselectrolyte secondary battery.

In addition, recently, application of the coin-type nonaqueouselectrolyte secondary battery, for example, to a power supply of anelectric vehicle, an auxiliary electric power storage unit of an energyconverting and storage system, and the like has been examined.Particularly, in a case where a lithium manganese oxide is used as apositive electrode active material, and a silicon oxide (SiO_(X)) isused as a negative electrode active material, it is possible to obtain anonaqueous electrolyte secondary battery in which charging anddischarging characteristics are excellent with a high energy density,and a cycle lifetime is long.

Here, in a case where a non-reflow type nonaqueous electrolyte secondarybattery of the related art is used for backup of a memory of a portablephone or a digital camera, an operation guarantee temperature range is−20° C. to 60° C. On the other hand, recently, realization of anonaqueous electrolyte secondary battery, which can be used for anelectronic component of an in-vehicle component such as a drive recorderunder a high-temperature environment of 80° C. or higher, has beenexpected. However, when the nonaqueous electrolyte secondary battery isused under the high-temperature environment, an electrolytic solutioninside the battery volatilizes, and lithium deteriorates due tointrusion of moisture into the battery, and thus there is a problem inthat capacity greatly deteriorates.

To suppress the volatilization of the electrolytic solution from theinside of the nonaqueous electrolyte secondary battery under thehigh-temperature environment or the intrusion of moisture into theinside of the battery as described above, there is suggested atechnology of setting a region, in which a compression ratio of thegasket interposed between the positive electrode casing and the negativeelectrode casing is in a predetermined range, at two or more sitesaround the entire periphery of the gasket (for example, refer toJP-A-58-135569).

In addition, with regard to the nonaqueous electrolyte secondarybattery, there is suggested a technology in which the compression ratioof the gasket interposed between the positive electrode casing and thenegative electrode casing is set to a predetermined range at three-pointpositions between a tip end of the positive electrode casing and thenegative electrode casing, between a tip end of the negative electrodecasing and the positive electrode casing, and between a folded tip endof the negative electrode casing and the positive electrode casing, andthe magnitudes of compression ratios at the respective three-pointpositions are set in this order (for example, refer to JP-A-9-283102).

JP-A-58-135569 and JP-A-9-283102 disclose that when the compressionratio of the gasket interposed between the positive electrode casing andthe negative electrode casing is set to a predetermined range, thefollowing effects can be expected. Specifically, sealing properties ofthe nonaqueous electrolyte secondary battery can be raised, leakage ofan electrolytic solution can be suppressed, and intrusion of moisturecan be suppressed.

SUMMARY OF THE INVENTION

However, when only the compression ratio of the gasket is defined asdescribed in JP-A-58-135569 and JP-A-9-283102, in a case where thenonaqueous electrolyte secondary battery is used or stored under ahigh-temperature environment, a gap occurs between the positiveelectrode casing or the negative electrode casing and the gasket asillustrated in a schematic cross-sectional view of FIG. 6, and thus itis still difficult to effectively prevent volatilization of theelectrolytic solution and intrusion of moisture into the inside of thebattery.

On the other hand, for example, the following configuration may beconsidered. Specifically a gap between the positive electrode casing andthe negative electrode casing may be set to be narrower to increase thecompression ratio of the gasket so as to further raise the sealingproperties of the battery. However, when the compression ratio of thegasket is set to be too high, there is a concern that the gasket may befractured, particularly, under a high-temperature environment.Accordingly, there is a problem in that the sealing properties of thebattery deteriorate due to fracturing of the gasket. That is, it isdifficult to improve the sealing properties of the battery during use orstorage under a high-temperature environment by simply increasing thecompression ratio of the gasket interposed between the positiveelectrode casing and the negative electrode casing. Accordingly, it canbe said that any technology capable of effectively preventingvolatilization of the electrolytic solution, intrusion of moisture intothe inside of the battery, and the like is not disclosed.

The invention has been made in consideration of the above-describedproblems, and an object thereof is to provide a nonaqueous electrolytesecondary battery in which occurrence of a gap between a positiveelectrode casing or a negative electrode casing and a gasket issuppressed to improve sealing properties of the battery, and thusvolatilization of an electrolytic solution or intrusion of moisture intothe inside of the battery can be effectively prevented, batterycharacteristics do not deteriorate and sufficient discharging capacitycan be retained under a high-temperature environment, the dischargingcapacity is large, and excellent storage characteristics are provided.

To solve the above-described problems, the present inventors have made athorough experimental investigation. As a result, they have obtained thefollowing finding. Specifically, when defining a position of a caulkingtip end in an opening of the positive electrode casing that constitutesthe secondary battery, a shape and dimensions of a side surface portionof the positive electrode casing, and a size relationship between thenonaqueous electrolyte secondary battery and the positive electrodecasing instead of defining a compression ratio of a gasket interposedbetween the positive electrode casing and the negative electrode casingsimilar to the related art, the compression ratio of the gasketinterposed between the positive electrode casing and the negativeelectrode casing also become appropriate, and thus sealing propertiescan be effectively improved. According to this, the present inventorshave found that volatilization of an electrolytic solution or intrusionof moisture into the inside of the battery can be prevented, and highbattery characteristics can be retained even under a high-temperatureenvironment, and they have accomplished the invention.

That is, according to an aspect of the invention, there is provided anonaqueous electrolyte secondary battery including a bottomedcylindrical positive electrode casing, and a negative electrode casingwhich is fixed to an opening of the positive electrode casing through agasket, and forms an accommodation space between the positive electrodecasing and the negative electrode casing. The opening of the positiveelectrode casing is caulked to the negative electrode casing side toseal the accommodation space. The caulking is performed in such a mannerthat a caulking tip end in the opening of the positive electrode casingis disposed in an inward direction of the negative electrode casing thana tip end of the negative electrode casing. A diameter d of thenonaqueous electrolyte secondary battery is in a range of 6.6 mm to 7.0mm, a height h1 of the nonaqueous electrolyte secondary battery is in arange of 1.9 mm to 2.3 mm, at least a part of a side surface portion ofthe positive electrode casing on an opening side is formed in a curvedsurface shape, a radius of curvature R of the curved surface is set in arange of 0.8 mm to 1.1 mm, and a height h2 of the positive electrodecasing is in a range of 65% to 73% with respect to the height h1 of thenonaqueous electrolyte secondary battery.

According to the invention, in the nonaqueous electrolyte secondarybattery having the above-described size, when the caulking tip end inthe opening of the positive electrode casing is disposed in an inwarddirection of the negative electrode casing than the tip end of thenegative electrode casing, and the size of the nonaqueous electrolytesecondary battery, the radius of curvature R of the side surface portionof the positive electrode casing, and a size relationship between thenonaqueous electrolyte secondary battery and the positive electrodecasing are respectively set in the above-described ranges, it ispossible to reliably press the negative electrode casing by the positiveelectrode casing, and it is possible to compress the gasket at asufficient compression ratio, and thus sealing conditions are defined inan appropriate range. According to this, even when the nonaqueouselectrolyte secondary battery is used or stored under a high-temperatureenvironment, occurrence of a gap between the positive electrode casingor the negative electrode casing and the gasket is suppressed, andsealing properties of the battery can be improved. Accordingly, it ispossible to prevent volatilization of an electrolytic solution andintrusion of moisture in the air to the inside of the battery, and thusit is possible to realize a nonaqueous electrolyte secondary batteryexcellent in storage characteristics.

In addition, in the nonaqueous electrolyte secondary battery configuredas described above, the gasket may be formed from any one of apolypropylene resin, polyphenylene sulfide (PPS), and a polyether etherketone (PEEK) resin.

When the gasket is configured by any one of the above-described resinmaterials, it is possible to prevent the gasket from being significantlydeformed during use or storage under a high-temperature environment, andsealing properties of the nonaqueous electrolyte secondary battery arefurther improved.

In addition, in the nonaqueous electrolyte secondary battery configuredas described above, a configuration in which a positive electrode whichis provided on the positive electrode casing side and includes a lithiumcompound as a positive electrode active material, a negative electrodewhich is provided on the negative electrode casing side and includesSiO_(X) (0≤X<2) as a negative electrode active material, a separatorwhich is disposed between the positive electrode and the negativeelectrode, and an electrolytic solution which fills the accommodationspace and includes at least an organic solvent and a supporting salt isaccommodated in the accommodation space may be employed.

When employing a configuration including a lithium compound as thepositive electrode active material and SiO_(X) (0≤X<2) or a lithiumcompound as a negative electrode active material similar to theabove-described configuration, it is possible to realize a nonaqueouselectrolyte secondary battery which is capable of obtaining higherdischarging capacity even in the case of being used or stored under ahigh-temperature environment.

In the nonaqueous electrolyte secondary battery configured as describedabove, the positive electrode active material preferably includes alithium manganese oxide or a lithium titanate.

When using the above-described compound as the positive electrode activematerial, even in the case of being used or stored under ahigh-temperature environment, it is possible to realize a nonaqueouselectrolyte secondary battery in which a reaction between theelectrolytic solution and the electrodes is suppressed in a charging anddischarging cycle, and thus a decrease in capacity can be prevented andhigher discharging capacity can be obtained.

In addition, in the nonaqueous electrolyte secondary battery configuredas described above, a configuration in which capacity balance (negativeelectrode capacity (mAh)/positive electrode capacity (mAh)), which isexpressed by capacity of the negative electrode and capacity of thepositive electrode, is in a range of 1.43 to 2.51 may be employed.

When the capacity balance between the positive electrode and thenegative electrode is set to the above-described range, and apredetermined margin is secured for the capacity on a negative electrodeside, even when decomposition due to a battery reaction quicklyprogresses, it is possible to secure a negative electrode capacity of acertain value or more. According to this, even when the nonaqueouselectrolyte secondary battery is stored or used for a long period oftime under a strict high-temperature and high-humidity environment, adecrease in discharging capacity does not occur, and storagecharacteristics are improved.

In addition, in the nonaqueous electrolyte secondary battery configuredas described above, a configuration in which the negative electrodeactive material may include lithium (Li) and SiO_(X) (0≤X<2), and amolar ratio (Li/SiO_(X)) between lithium and SiO_(X) is in a range of3.9 to 4.9 may be employed.

When the negative electrode active material is configured by lithium(Li) and SiO_(X), and a molar ratio thereof is set to theabove-described range, it is possible to prevent charging abnormalityand the like, and even in the case of being used or stored for a longperiod of time under a high-temperature environment, a decrease indischarging capacity does not occur, and storage characteristics areimproved.

In addition, in the nonaqueous electrolyte secondary battery configuredas described above, in the electrolytic solution, the organic solvent ispreferably a mixed solvent which contains propylene carbonate (PC) thatis a cyclic carbonate solvent, ethylene carbonate (EC) that is a cycliccarbonate solvent, and dimethoxy ethane (DME) that is a chain ethersolvent.

When the organic solvent that is used in the electrolytic solution isset to the mixed solvent of respective compositions similar to theabove-described configuration, it is possible to retain sufficientdischarging capacity in a broad temperature range also including ahigh-temperature environment.

Specifically, first, when using PC and EC which have a high dielectricconstant and high solubility for the supporting salt as the cycliccarbonate solvent, it is possible to obtain large discharging capacity.In addition, it is possible to obtain an electrolytic solution that isless likely to volatilize even in the case of being used or stored undera high-temperature environment when considering that PC and EC have ahigh boiling point.

In addition, when PC, which has a melting point lower than that of EC,and EC are mixed and used as the cyclic carbonate solvent, it ispossible to improve low-temperature characteristics.

In addition, when DME having a low melting point is used as the chainether solvent, low-temperature characteristics are improved. Inaddition, DME has low viscosity, and thus electrical conductivity of theelectrolytic solution is improved. In addition, DME solvates with Liions, and thus it is possible to obtain large discharging capacity asthe nonaqueous electrolyte secondary battery.

In addition, in the nonaqueous electrolyte secondary battery configuredas described above, in the organic solvent, a mixing ratio between thepropylene carbonate (PC), the ethylene carbonate (EC), and the dimethoxyethane (DME) is more preferably (PC:EC:DME)=0.5 to 1.5:0.5 to 1.5:1 to 3in terms of a volume ratio.

When a mixing ratio of the organic solvent that is used in theelectrolytic solution is defined in an appropriate range similar to theabove-described configuration, it is possible to attain a significanteffect of improving low-temperature characteristics withoutdeteriorating the above-described capacity retention under ahigh-temperature.

In addition, in the nonaqueous electrolyte secondary battery configuredas described above, in the electrolytic solution, the supporting salt ispreferably lithium bis(trifluoromethane) sulfonimide (Li(CF₃SO₂)₂N).

When the supporting salt that is used in the electrolytic solution isset to the above-described lithium compound, it is possible to obtainsufficient discharging capacity in a broad temperature range alsoincluding a high-temperature environment, and characteristics of thenonaqueous electrolyte secondary battery are improved.

In addition, in the nonaqueous electrolyte secondary battery configuredas described above, a configuration in which the separator is formedfrom glass fiber may be employed.

When the separator is configured by the glass fiber, internal resistanceof the nonaqueous electrolyte secondary battery is reduced anddischarging capacity is further improved when considering that aseparator having excellent mechanical strength and large ionpermeability can be obtained.

According to the nonaqueous electrolyte secondary battery of theinvention, as described above, when the caulking tip end in the openingof the positive electrode casing is disposed in an inward direction thanthe tip end of the negative electrode casing, and the size of thenonaqueous electrolyte secondary battery, the radius of curvature R ofthe side surface portion of the positive electrode casing, and a sizerelationship between the nonaqueous electrolyte secondary battery andthe positive electrode casing are respectively set in theabove-described ranges, it is possible to reliably press the negativeelectrode casing by the positive electrode casing, and it is possible tocompress the gasket at a sufficient compression ratio, and thus sealingconditions are defined in an appropriate range.

According to this, even when the nonaqueous electrolyte secondarybattery having a size in which the diameter d is in a range of 6.6 mm to7.0 mm, and a height h1 is in a range of 1.9 mm to 2.3 mm is used orstored under a high-temperature environment, occurrence of a gap betweenthe positive electrode casing or the negative electrode casing and thegasket is suppressed, and thus sealing properties of the battery can beimproved. As a result, volatilization of an electrolytic solution orintrusion of moisture in the air to the inside of the battery can beeffectively prevented.

Accordingly, it is possible to provide a nonaqueous electrolytesecondary battery in which even under a high-temperature environment,battery characteristics do not deteriorate, sufficient dischargingcapacity can be retained, discharging capacity is large, and excellentstorage characteristics are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a nonaqueouselectrolyte secondary battery according to an embodiment of theinvention;

FIG. 2 is a schematic cross-sectional view illustrating the nonaqueouselectrolyte secondary battery according to the embodiment of theinvention, and illustrates an enlarged view of main portions illustratedin FIG. 1;

FIG. 3 is a schematic cross-sectional view illustrating an example ofthe nonaqueous electrolyte secondary battery according to the embodimentof the invention;

FIG. 4 is a schematic cross-sectional view illustrating a comparativeexample that is a nonaqueous electrolyte secondary battery having aconfiguration of the related art;

FIG. 5 is a schematic cross-sectional view illustrating an internalstate of the battery after a radius of curvature R of a side surfaceportion of a positive electrode casing provided to the nonaqueouselectrolyte secondary battery is appropriately changed, and ahigh-temperature and high-humidity test is performed; and

FIG. 6 is a schematic cross-sectional view illustrating a nonaqueouselectrolyte secondary battery of the related art.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a configuration of a nonaqueous electrolyte secondarybattery according to an embodiment of the invention will be described indetail as an example with reference to FIGS. 1 and 2. In addition,specifically, the nonaqueous electrolyte secondary battery described inthe invention is a nonaqueous electrolyte secondary battery in which anactive material used as a positive electrode or a negative electrode,and an electrolytic solution are accommodated in a container.

Nonaqueous Electrolyte Secondary Battery

A nonaqueous electrolyte secondary battery 1 according to an embodimentof the invention as illustrated in FIGS. 1 and 2 is a so-calledcoin-type (button-type) battery. The nonaqueous electrolyte secondarybattery 1 includes a positive electrode 10 that is capable ofintercalating and deintercalating lithium ions, a negative electrode 20that is capable of intercalating and deintercalating lithium ions, athat is disposed between the positive electrode 10 and the negativeelectrode 20, and an electrolytic solution 50 that includes at least asupporting salt and an organic solvent in an accommodation container 2.

More specifically, the nonaqueous electrolyte secondary battery 1includes an accommodation container 2. The accommodation container 2includes a bottomed cylindrical positive electrode casing 12, and acovered cylindrical (hat-shaped) negative electrode casing 22 which isfixed to an opening 12 a of the positive electrode casing 12 through agasket 40 and forms an accommodation space between the positiveelectrode casing 12 and the negative electrode casing 22. Theaccommodation space is sealed by caulking the peripheral edge of theopening 12 a of the positive electrode casing 12 to an inner side, thatis, to the negative electrode casing 22 side.

In the accommodation space sealed by the accommodation container 2, thepositive electrode 10 that is provided on the positive electrode casing12 side, and the negative electrode 20 that is provided on the negativeelectrode casing 22 side are disposed to face each other through theseparator 30. In addition, the electrolytic solution 50 fills theaccommodation container 2. In addition, in an example illustrated inFIG. 1, lithium foil 60 is interposed between the negative electrode 20and the separator 30.

In addition, as illustrated in FIG. 1, the gasket 40 is inserted alongan inner peripheral surface of the positive electrode casing 12, and isconnected to the outer periphery of the separator 30 to support theseparator 30.

In addition, the positive electrode 10, the negative electrode 20, andthe separator 30 are impregnated with the electrolytic solution 50 thatfills the accommodation container 2.

In the nonaqueous electrolyte secondary battery 1 of the exampleillustrated in FIG. 1, the positive electrode 10 is electricallyconnected to an inner surface of the positive electrode casing 12through a positive electrode current collector 14, and the negativeelectrode 20 is electrically connected to an inner surface of thenegative electrode casing 22 through a negative electrode currentcollector 24. In this embodiment, the nonaqueous electrolyte secondarybattery 1, which includes the positive electrode current collector 14and the negative electrode current collector 24, illustrated in FIG. 1is described as an example. However, there is no limitation thereto, andfor example, a configuration, in which the positive electrode casing 12also serves as a positive electrode current collector and the negativeelectrode casing 22 also serves as the negative electrode currentcollector, may be employed.

The nonaqueous electrolyte secondary battery 1 of this embodiment isschematically configured as described above, and lithium ions migratefrom one side of the positive electrode 10 and the negative electrode 20to the other side thereof, and thus electric charges can be stored(charged) or emitted (discharged).

Positive Electrode Casing and Negative Electrode Casing

In this embodiment, the positive electrode casing 12 that constitutesthe accommodation container 2 is configured in a bottomed cylindricalshape as described above, and has the opening 12 a having a circularshape when viewed in a plan view. As a material of the positiveelectrode casing 12, a material, which is known in the related art, maybe used without any limitation, and examples thereof include stainlesssteel such as NAS64.

In addition, the negative electrode casing 22 is configured in a coveredcylindrical shape (hat shape) as described above, and has aconfiguration that a tip end 22 a thereof is inserted into the positiveelectrode casing 12 from the opening 12 a. Examples of a material of thenegative electrode casing 22 include stainless steel, which is known inthe related art, similar to the material of the positive electrodecasing 12, and for example, SUS304-BA and the like may be used. Inaddition, for example, a clad material, which is obtained bypressure-welding copper, nickel, or the like to the stainless steel, maybe also used as the negative electrode casing 22.

As illustrated in FIG. 1, in a state in which the gasket 40 isinterposed between the positive electrode casing 12 and the negativeelectrode casing 22, the peripheral edge of the opening 12 a of thepositive electrode casing 12 is caulked to the negative electrode casing22 side and is fixed thereto, and thus the nonaqueous electrolytesecondary battery 1 is sealed and is retained in a state in which theaccommodation space is formed. Accordingly, the maximum inner diameterof the positive electrode casing 12 is set to a dimension larger thanthe maximum outer diameter of the negative electrode casing 22.

In addition, in the nonaqueous electrolyte secondary battery 1 of thisembodiment, a sealing shape between the positive electrode casing 12 andthe negative electrode casing 22, which are fixed to each to each otherthrough the gasket 40 as illustrated in FIG. 2, is configured byadjusting a dispositional relationship and a dimensional relationshipbetween the nonaqueous electrolyte secondary battery 1, the positiveelectrode casing 12 and the negative electrode casing 22. Specifically,the sealing shape is configured to satisfy the following dispositionalrelationships and dimensional relationships of (1) to (3).

(1) A caulking tip end 12 b in the opening 12 a of the positiveelectrode casing 12 is disposed in an inward direction of the negativeelectrode casing 22 than the tip end 22 a of the negative electrodecasing 22.

(2) A diameter d of the nonaqueous electrolyte secondary battery 1 is ina range of 6.6 mm to 7.0 mm, and a height h1 thereof is in a range of1.9 mm to 2.3 mm.

(3) At least a part of a side surface portion 12 d of the positiveelectrode casing 12 on an opening 12 a side is formed in a curvedsurface shape, a radius of curvature R of the curved surface is set in arange of 0.8 mm to 1.1 mm, and a height h2 of the positive electrodecasing 12 is in a range of 65% to 73% with respect to the height h1 ofthe nonaqueous electrolyte secondary battery 1.

In the nonaqueous electrolyte secondary battery 1 of this embodiment, asillustrated in FIG. 2, the caulking tip end 12 b in the opening 12 a ofthe positive electrode casing 12 is disposed in an inward direction ofthe negative electrode casing 22 than the tip end 22 a of the negativeelectrode casing 22, and the size of the nonaqueous electrolytesecondary battery 1, the radius of curvature R of the side surfaceportion 12 d of the positive electrode casing 12, and the sizerelationship between the nonaqueous electrolyte secondary battery 1 andthe positive electrode casing 12 are respectively set in theabove-described ranges, and thus disposition and sealing conditions ofthe gasket 40 are defined in an appropriate range. According to this,occurrence of a gap between the positive electrode casing 12 or thenegative electrode casing 22 and the gasket 40 is suppressed even in thecase of use or storage for a long period of time under ahigh-temperature environment, and thus the sealing properties of thenonaqueous electrolyte secondary battery 1 are improved. As a result,volatilization of the electrolytic solution 50 to the outside of thebattery, or intrusion of moisture, which is included in the air, intothe battery can be reliably prevented, and thus it is possible to obtainthe nonaqueous electrolyte secondary battery 1 which has high capacityretention ratio and excellent storage characteristics under ahigh-temperature environment.

More specifically, as described above in (1), when the opening 12 a ofthe positive electrode casing 12 is caulked and sealed, the caulking tipend 12 b of the positive electrode casing 12 is located in an inwarddirection than a maximum outer diameter portion of the negativeelectrode casing 22. Accordingly, it is possible to reliably press thenegative electrode casing 22 by the positive electrode casing 12, and itis possible to compress the gasket 40 at a sufficient compression ratio.

In addition, when the entire dimensions of the nonaqueous electrolytesecondary battery 1 are defined as described above in (2), and then theradius of curvature R of the side surface portion 12 d of the positiveelectrode casing 12 is set to the above-described range as describedabove in (3), as described above, the negative electrode casing 22 isreliably pressed by the positive electrode casing 12, and thus it ispossible to significantly obtain an effect capable of compressing thegasket 40 at a sufficient compression rate.

Here, when the radius of curvature R of the side surface portion 12 dexceeds 1.1 mm, a force with which the positive electrode casing 12presses the negative electrode casing 22 from an upper side becomesweak, and thus the compression ratio of the gasket 40 decreases at aposition of the bottom 12 c. In addition, the height h2 of the positiveelectrode casing 12 tends to vary, and thus a variation in internalresistance increases.

In addition, when the radius of curvature R of the side surface portion12 d is less than 0.8 mm, a force with which the positive electrodecasing 12 presses the negative electrode casing 22 from a side directionbecomes weak, and thus the compression ratio of the gasket 40 decreasesat a position of the side surface portion 22 b of the negative electrodecasing.

In addition, when the entire dimensions of the nonaqueous electrolytesecondary battery 1 are defined as described above in (2), and then theheight h2 of the positive electrode casing 12 is set to theabove-described range with respect to the height h1 of the nonaqueouselectrolyte secondary battery 1 as described above in (3), as describedabove, the negative electrode casing 22 is reliably pressed by thepositive electrode casing 12, and thus it is possible to furthersignificantly obtain an effect capable of compressing the gasket 40 at asufficient compression rate.

Here, when the ratio of the height h2 of the positive electrode casing12 to the height h1 of the nonaqueous electrolyte secondary battery 1exceeds 73%, in the battery size of this embodiment, a force with whichthe positive electrode casing 12 presses the negative electrode casing22 from an upper side becomes weak, and thus there is a concern that thecompression ratio of the gasket 40 decreases at a position of the bottom12 c.

In addition, when the ratio of the height h2 of the positive electrodecasing 12 to the height h1 of the nonaqueous electrolyte secondarybattery 1 is less than 65%, the compression ratio of the gasket 40becomes excessive and fracturing occurs, and thus there is a possibilitythat short-circuit between the positive electrode casing 12 and thenegative electrode casing 22, and the like may occur.

In addition, in the nonaqueous electrolyte secondary battery 1 of thisembodiment, typically, a sheet thickness of a metal sheet material thatis used in the positive electrode casing 12 or the negative electrodecasing 22 is approximately 0.1 mm to 0.3 mm, and for example, an averagesheet thickness t of the positive electrode casing 12 or the negativeelectrode casing 22 may be set to approximately 0.15 mm.

In addition, in the example illustrated in FIGS. 1 and 2, the tip end 22a of the negative electrode casing 22 has a folded-back shape, but thereis no limitation thereto. For example, the invention is also applicableto a shape which does not have a folded-back shape and in which an endsurface of a metal sheet material is set as the tip end 22 a.

In addition, as described above, the configuration of the invention, inwhich the sealing conditions are defined by the dispositionalrelationship and the dimensional relationship between the positiveelectrode casing 12 and the negative electrode casing 22 of thenonaqueous electrolyte secondary battery 1, is applicable to a coin type(621 size) nonaqueous electrolyte secondary battery in which thediameter d is in a range of 6.6 mm to 7.0 mm, and the height h1 is in arange of 1.9 mm to 2.3 mm.

Here, in the nonaqueous electrolyte secondary battery 1 that isdescribed in this embodiment, particularly, the height h2 of thepositive electrode casing 12 is in a range of 65% to 73% with respect tothe entire height h1 of the nonaqueous electrolyte secondary battery 1,and thus it is possible to reliably perform holding-down of the negativeelectrode casing 22 by caulking the positive electrode casing 12 duringsealing. That is, in the nonaqueous electrolyte secondary battery 1, aratio of (the height h2 of the positive electrode casing)/(the height h1of the nonaqueous electrolyte secondary battery) is set in the definedrange, and thus occurrence of a gap between the positive electrodecasing 12 or the negative electrode casing 22 and the gasket 40 issuppressed even in the case of use or storage for a long period of timeunder a high-temperature environment, and thus it is possible tosignificantly obtain an effect of improving the sealing properties ofthe nonaqueous electrolyte secondary battery 1.

Gasket

As illustrated in FIG. 1, the gasket 40 is formed in an annular ringshape along the inner peripheral surface of the positive electrodecasing 12, and the tip end 22 a of the negative electrode casing 22 isdisposed inside an annular groove 41 of the gasket 40.

In addition, for example, it is preferable that a material of the gasket40 be a resin in which a heat deformation temperature is 230° C. orhigher. When the heat deformation temperature of the resin material thatis used in the gasket 40 is 230° C. or higher, even when the nonaqueouselectrolyte secondary battery 1 is used or stored under ahigh-temperature environment, or even when heat generation occurs duringuse of the nonaqueous electrolyte secondary battery 1, it is possible toprevent the gasket from being significantly deformed, and thus it ispossible to prevent the electrolytic solution 50 from leaking.

Examples of a material of the gasket 40 include plastic resins such as apolypropylene resin (PP), polyphenylene sulfide (PPS), polyethyleneterephthalate (PET), polyamide, a liquid crystal polymer (LCP), atetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA), apolyether ether ketone resin (PEEK), a polyether nitrile resin (PEN), apolyether ketone resin (PEK), a polyarylate resin, a polybutyleneterephthalate resin (PBT), a polycyclohexane dimethylene terephthalateresin, a polyether sulfone resin (PES), a polyamino bismaleimide resin,a polyether imide resin, and a fluorine resin. Among these, it ispreferable to use any one of PP, PPS, and PEEK in the gasket 40 whenconsidering that it is possible to prevent the gasket from beingsignificantly deformed during use or storage under a high-temperatureenvironment, and the sealing properties of the nonaqueous electrolytesecondary battery are further improved.

In addition, in the gasket 40, a material, which is obtained by mixingglass fiber, mica whiskers, ceramic fine powders, and the like to theabove-described material in an added amount of 30 mass % or less, may beappropriately used. When using this material, it is possible to preventsignificant deformation of the gasket due to a high-temperature andleakage of the electrolytic solution 50.

In addition, a sealing agent may be further applied onto an inner sidesurface of the annular groove of the gasket 40. As the sealing agent,asphalt, an epoxy resin, a polyamide-based resin, a butyl rubber-basedadhesive, and the like may be used. In addition, after being appliedonto the inside of the annular groove 41, the sealing agent is dried.

In addition, in the nonaqueous electrolyte secondary battery 1 of thisembodiment, it is preferable to adjust the compression ratio of thegasket 40 after the caulking tip end 12 b of the positive electrodecasing 12 is disposed in an inward direction than the tip end 22 a ofthe negative electrode casing 22, and the size of the nonaqueouselectrolyte secondary battery 1, the radius of curvature R of the sidesurface portion 12 d of the positive electrode casing 12, and the sizerelationship between the nonaqueous electrolyte secondary battery 1 andthe positive electrode casing 12 are respectively defined as describedabove. Specifically, it is preferable that the compression ratio of thegasket 40 at positions of G1 to G3 illustrated in FIG. 2, that is,respective sites to be described below be equal to or more than 50%.

G1: Position with the shortest distance between the caulking tip end 12b of the positive electrode casing 12 and the negative electrode casing22 in the opening 12 a of the positive electrode casing 12.

G2: Position with the shortest distance between the tip end 22 a of thenegative electrode casing 22 and the positive electrode casing 12.

G3: Position between the tip end 22 a of the negative electrode casing22 and the bottom 12 c of the positive electrode casing 12.

In this embodiment, as described above, when the compression ratio ofthe gasket 40 is adjusted in addition to the definition of thedispositional relationship and the dimensional relationship between thenonaqueous electrolyte secondary battery 1, the positive electrodecasing 12, and the negative electrode casing 22, it is possible to morereliably improve the sealing properties of the nonaqueous electrolytesecondary battery, and particularly, in a case of use or storage under ahigh-temperature environment, it is possible to attain more significantsealing properties.

In addition, the upper limit of the compression ratio of the gasket 40is not particularly limited, but when the upper limit is set to be equalto or less than 95%, it is possible to retain satisfactory sealingproperties without fracture of the gasket 40 under a high-temperatureenvironment.

Electrolytic Solution

In the nonaqueous electrolyte secondary battery 1 of this embodiment, asthe electrolytic solution 50, an electrolytic solution including atleast an organic solvent and a supporting salt is used. In addition, inthe electrolytic solution 50, it is preferable to use a mixed solvent,which contains propylene carbonate (PC) that is a cyclic carbonatesolvent, ethylene carbonate (EC) that is a cyclic carbonate solvent, anddimethoxy ethane (DME) that is a chain ether solvent, as the organicsolvent.

Typically, the electrolytic solution has a configuration in which thesupporting salt is dissolved in a nonaqueous solvent such as an organicsolvent, and characteristics of the electrolytic solution are determinedin consideration of heat resistance, viscosity, and the like which aredemanded for the electrolytic solution.

Generally, in a case of using the electrolytic solution, which uses theorganic solvent, in the nonaqueous electrolyte secondary battery,temperature dependency of conductivity increases when considering thatsolubility of a lithium salt is deficient, and thus there is a problemin that characteristics at a low temperature greatly decrease incomparison to characteristics at room temperature. On the other hand, toimprove low-temperature characteristics, for example, in a case of usingethyl methyl carbonate or acetic acid esters which have an asymmetricstructure and are chain carbonic acid esters as the organic solvent ofthe electrolytic solution, there is a problem in that thecharacteristics of the nonaqueous electrolyte secondary battery at ahigh temperature conversely decrease. In addition, even in a case ofusing an organic solvent such as ethyl methyl carbonate in theelectrolytic solution, solubility of a lithium salt is also deficient,and there is a limit to improvement of the low-temperaturecharacteristics.

In contrast, in this embodiment, the organic solvent, which is used inthe electrolytic solution 50, is set to a mixed solvent that contains PCand EC which are cyclic carbonate solvents, and DME that is a chainether solvent. Accordingly, it is possible to realize the nonaqueouselectrolyte secondary battery 1 which is capable of retaining sufficientdischarging capacity in a broad temperature range including thehigh-temperature environment.

Specifically, first, as the cyclic carbonate solvent, PC and EC whichhave a high dielectric constant and high solubility for the supportingsalt are used, and thus it is possible to obtain large dischargingcapacity. In addition, it is possible to obtain an electrolytic solutionthat is less likely to volatilize even in the case of being used orstored under a high-temperature environment when considering that PC andEC have a high boiling point.

In addition, when PC, which has a melting point lower than that of EC,and EC are mixed and used as the cyclic carbonate solvent, it ispossible to improve low-temperature characteristics.

In addition, when DME having a low melting point is used as the chainether solvent, low-temperature characteristics are improved. Inaddition, DME has low viscosity, and thus electrical conductivity of theelectrolytic solution is improved. In addition, DME solvates with Liions, and thus it is possible to obtain large discharging capacity asthe nonaqueous electrolyte secondary battery.

The cyclic carbonate solvent has a structure (Chemical Formula 1) to bedescribed below, and examples thereof include propylene carbonate (PC),ethylene carbonate (EC), butylene carbonate (BC), trifluoroethylenecarbonate (TFPC), chloroethylene carbonate (CIEC), trifluoroethylenecarbonate (TFEC), difluoroethylene carbonate (DFEC), vinylene carbonate(VEC), and the like. In this embodiment, particularly, from theviewpoint of improvement of capacity retention ratio at ahigh-temperature in addition to the viewpoints of easiness of filmformation on an electrode onto the negative electrode 20 and improvementof low-temperature characteristics, two kinds including PC and EC areused as the cyclic carbonate solvent having the structure (ChemicalFormula 1) to be described below.

However, in Chemical Formula 1, R1, R2, R3, and R4 represent any one ofhydrogen, fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms,and a fluorinated alkyl group. In addition, in Chemical Formula 1, R1,R2, R3, and R4 may be the same as each other or different from eachother.

In this embodiment, as described above, when using PC and EC which havea high dielectric constant and high solubility for the supporting saltas the cyclic carbonate solvent, it is possible to obtain largedischarging capacity. In addition, it is possible to obtain anelectrolytic solution that is less likely to volatilize even in the caseof being used or stored under a high-temperature environment whenconsidering that PC and EC have a high boiling point. In addition, whenPC, which has a melting point lower than that of EC, and EC are mixedand used as the cyclic carbonate solvent, it is possible to obtainexcellent low-temperature characteristics.

The chain ether solvent has a structure expressed by Chemical Formula 2to be described below, and examples thereof include 1,2-dimethoxy ethane(DME), 1,2-diethoxy ethane (DEE), and the like. In this embodiment,particularly, DME that tends to solvate with lithium ions is used as thechain ether solvent having the structure expressed by Chemical Formula 2to be described below particularly from the viewpoints of improving thelow-temperature characteristics while securing capacity at roomtemperature in addition to the viewpoint of improving conductivity.

However, in Chemical Formula 2, R5 and R6 represent any one of hydrogen,fluorine, chlorine, an alkyl group having 1 to 3 carbon atoms, and afluorinated alkyl group. In addition, R5 and R6 may be the same as eachother or different from each other.

In this embodiment, as described above, when DME having a low meltingpoint is used as the chain ether solvent, the low-temperaturecharacteristics are improved. In addition, DME has low viscosity, andthus electrical conductivity of the electrolytic solution is improved.In addition, DME solvates with Li ions, and thus it is possible toobtain large discharging capacity as the nonaqueous electrolytesecondary battery.

In the electrolytic solution 50, a mixing ratio of respective solventsin the organic solvent is not particularly limited. However, it ispreferable that the mixing ratio be, for example, in a range of(PC:EC:DME)=0.5 to 1.5:0.5 to 1.5:1 to 3 in terms of a volume ratio,more preferably in a range of 0.8 to 1.2:0.8 to 1.2:1.5 to 2.5, andstill more preferably (PC:EC:DME)=(1:1:2).

When the mixing ratio of the organic solvent is in the above-describedrange, it is possible to more significantly obtain the effect ofimproving the low-temperature characteristics without deteriorating thecapacity retention ratio at a high temperature.

Specifically, when a mixing ratio of the propylene carbonate (PC) thatis a cyclic carbonate solvent is equal to or more than the lower limitof the range, if PC having a melting point lower than that of EC and ECare mixed and used, it is possible to significantly obtain the effect ofimproving the low-temperature characteristics.

On the other hand, PC has a dielectric constant lower than that of EC,and thus it is difficult for PC to increase a concentration of thesupporting salt. Therefore, when an amount of PC is too large, it may bedifficult to obtain large discharging capacity. Accordingly, it ispreferable to limit the mixing ratio of PC to a value equal to or lessthan the upper limit of the range.

In addition, in the organic solvent, when a mixing ratio of the ethylenecarbonate (EC) that is a cyclic carbonate solvent is equal to or morethan the lower limit of the range, it is possible to increase dielectricconstant of the electrolytic solution 50 and solubility for thesupporting salt, and it is possible to obtain large discharging capacityas the nonaqueous electrolyte secondary battery.

On the other hand, EC has high viscosity, and thus EC is deficient inelectrical conductivity. In addition, EC has a high melting point, andthus when an amount of EC is too large, the low-temperaturecharacteristics may decrease. Accordingly, it is preferable to limit themixing ratio thereof to a value equal to or less than the upper limit ofthe range.

In addition, in the organic solvent, when a mixing ratio of dimethoxyethane (DME) that is a chain ether solvent is set to be equal to or morethan the lower limit of the range, a predetermined amount of DME havinga low melting point is contained in the organic solvent, and thus it ispossible to significantly obtain the effect of improving thelow-temperature characteristics. In addition, DME has low viscosity, andthus electrical conductivity is improved. In addition, DME solvates withLi ions, and thus it is possible to obtain large discharging capacity.

On the other hand, DME has a low dielectric constant, and thus it isdifficult to increase a concentration of the supporting salt.Accordingly, when an amount of DME is too large, it may be difficult toobtain large discharging capacity, and thus it is preferable to limitthe mixing ratio of DME to a value equal to or less than the upper limitof the range.

As the supporting salt that is used in the electrolytic solution 50, aknown Li compound, which is added to the electrolytic solution as asupporting salt in the nonaqueous electrolyte secondary battery, may beused, and there is no particular limitation to the supporting salt.Examples of the supporting salt include lithium tetrafluoroborate,lithium bisperfluoromethylsulfonyl imide, lithiumbisperfluoroethylsulfonyl imide, lithium bistrifluoromethane sulfonimide(Li(CF₃SO₂)₂N), lithium hexafluorophosphate (LiPF₆), and the like inconsideration of thermal stability and the like. Among these, it ispreferable to use Li(CF₃SO₂)₂N) or LiPF₆ as the supporting salt whenconsidering that it is possible to increase heat resistance of theelectrolytic solution and it is possible to suppress a decrease incapacity at a high temperature.

In addition, the supporting salts may be used alone or in combination oftwo or more kinds thereof.

An amount of the supporting salt in the electrolytic solution 50 may bedetermined by the kind of the positive electrode active material to bedescribed below and in consideration of the kind of the supporting saltand the like. For example, the amount of the supporting salt ispreferably 0.1 mol/L to 3.5 mol/L, more preferably 0.5 mol/L to 3 mol/L,and still more preferably 1 mol/L to 2.5 mol/L. In addition, in a caseof using a lithium manganese oxide as the positive electrode activematerial, the amount of the supporting salt is preferably set toapproximately 1 mol/L, and in a case of using lithium titanate, theamount of the supporting salt is preferably set to approximately 1.4mol/L.

In addition, when the concentration of the supporting salt in theelectrolytic solution 50 is too high or too low, conductivitydeteriorates, and thus there is a concern that this decrease has anadverse effect on battery characteristics, and thus it is preferable toset the amount of the supporting salt in the above-described range.

In the nonaqueous electrolyte secondary battery 1 of this embodiment,after the caulking tip end 12 b of the positive electrode casing 12 isdisposed in an inward direction than the tip end 22 a of the negativeelectrode casing 22, and the size of the nonaqueous electrolytesecondary battery 1, the radius of curvature R of the side surfaceportion 12 d of the positive electrode casing 12, and the sizerelationship between the nonaqueous electrolyte secondary battery 1 andthe positive electrode casing 12 are defined as described above, theelectrolytic solution 50 having the above-described composition is used.Accordingly, even in a case of use or storage for a long period of timeunder a high-temperature environment, it is possible to retain highdischarging capacity, and retention characteristics become excellent.

In addition, in the nonaqueous electrolyte secondary battery 1 of thisembodiment, for example, when using an organic solvent obtained bymixing PC, EC, and DME in the mixing ratios as described above insteadof the electrolytic solution 50 having the above-described composition,as the supporting salt, a supporting salt, which contains at least anyof lithium bis(fluorosulfonyl) imide (LiFSI) and lithiumbis(trifluoromethanesulfonyl) imide (LiTFSI) in a total amount of 0.8mol/L to 1.2 mol/L, may be employed. When using the electrolyticsolution as described above, it is possible to more significantly obtainan effect of improving the low-temperature characteristics withoutdeteriorating the capacity retention ratio at a high temperature or roomtemperature. In addition, it is more preferable that as the supportingsalt, LiFSI having excellent conductivity is used alone, and iscontained in the electrolytic solution 50 in an amount of 0.8 mol/L to1.2 mol/L when considering that it is possible to suppress voltage dropat an initial stage of discharging, it is also possible to improvedischarging characteristics under a low-temperature environment, and asufficient discharging capacity is obtained in a wide temperature range.

Positive Electrode

In positive electrode 10, a kind of a positive electrode active materialis not particularly limited, and the positive electrode active materialincludes a lithium compound. A positive electrode active material thatis conventionally known in this field is used, and an active materialthat is obtained by mixing polyacrylic acid as a binding agent, graphiteas a conductive assistant, and the like may be used. Particularly, it ispreferable that the positive electrode contain at least one of a lithiummanganese oxide (Li₄Mn₅O₁₂), lithium titanate (Li₄Ti₅O₁₂), MoO₃,LiFePO₄, and Nb₂O₃ as the positive electrode active material. It is morepreferable that among these compounds, the positive electrode containthe lithium manganese oxide or the lithium titanate. In addition, withregard to the lithium manganese oxide, for example, a material, which isobtained by adding a transition metal element such as Co and Ni to thelithium manganese oxide expressed as Li_(1+x)Co_(y)Mn_(2-x-y)O₄(0≤x≤0.33, 0<y≤0.2), may also be used.

When the above-described positive electrode active material is used inthe positive electrode 10, particularly, a reaction between theelectrolytic solution 50 and the positive electrode 10 at a charging anddischarging cycle under a high-temperature environment is suppressed,and thus it is possible to prevent a decrease in capacity, and it ispossible to increase capacity retention ratio.

In addition, in this embodiment, not only one kind of theabove-described materials but also a plurality of kinds of theabove-described materials may be contained as the positive electrodeactive material.

In addition, in a case of using a granular positive electrode activematerial configured by the above-described material, a particle size(D50) is not particularly limited, and for example, a particle size of0.1 μm to 100 μm is preferable, and a particle size of 1 μm to 10 μm ismore preferable.

If the particle size (D50) of the positive electrode active material isless than the lower limit of the above-described preferable range, whenthe nonaqueous electrolyte secondary battery is exposed to a hightemperature, reactivity increases, and thus handling becomes difficult.In addition, when the particle size exceeds the upper limit thereof, adischarging rate may decrease.

In addition, the “particle size (D50) of the positive electrode activematerial” in the invention is a particle size measured by a laserdiffraction method and represents a median size.

An amount of the positive electrode active material in the positiveelectrode 10 is determined in consideration of discharging capacity andthe like that are demanded for the nonaqueous electrolyte secondarybattery 1, and the amount is preferably 50 mass % to 95 mass %. When theamount of the positive electrode active material is equal to or morethan the lower limit of the preferable range, it is easy to obtainsufficient discharging capacity. When the amount of the positiveelectrode active material is equal to or less than the upper limit ofthe preferable range, it is easy to form the positive electrode 10.

The positive electrode 10 may contain a conductive assistant(hereinafter, the conductive assistant that is used in the positiveelectrode 10 may be referred to as a “positive electrode conductiveassistant”).

Examples of the positive electrode conductive assistant includecarbonaceous materials such as furnace black, ketjen black, acetyleneblack, and graphite.

As the positive electrode conductive assistant, the above-describedcarbonaceous materials may be used alone or in combination of two ormore kinds thereof.

In addition, an amount of the positive electrode conductive assistant inthe positive electrode 10 is preferably 4 mass % to 40 mass %, and morepreferably 10 mass % to 25 mass %. When the amount of the positiveelectrode conductive assistant is equal to or more than the lower limitof the preferable range, it is easy to obtain sufficient conductivity.In addition, in a case of molding the electrode in a pellet shape,molding becomes easy. On the other hand, when the amount of the positiveelectrode conductive assistant in the positive electrode 10 is equal toor less than the upper limit of the preferable range, it is easy toobtain sufficient discharging capacity in the positive electrode 10.

The positive electrode 10 may contain a binder (hereinafter, the binderthat is used in the positive electrode 10 may be referred to as a“positive electrode binder”).

As the positive electrode binder, a material that is known in therelated art may be used, and examples thereof includepolytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),styrene-butadiene rubber (SBR), polyacrylic acid (PA), carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), and the like. Among these, thepolyacrylic acid is preferable, and a cross-linking type polyacrylicacid is more preferable.

In addition, as the positive electrode binder, the above-describedmaterials may be used alone or in combination of two or more kindsthereof.

In addition, in a case of using the polyacrylic acid as the positiveelectrode binder, it is preferable that the polyacrylic acid be adjustedin advance to pH 3 to pH 10. For the pH adjustment in this case, forexample, an alkali metal hydroxide such as lithium hydroxide, or analkali-earth metal hydroxide such as magnesium hydroxide may be used.

An amount of the positive electrode binder in the positive electrode 10may be set, for example, to 1 mass % to 20 mass %.

The size of the positive electrode 10 is determined in accordance withthe size of the nonaqueous electrolyte secondary battery 1.

In addition, the thickness of the positive electrode 10 is alsodetermined in accordance with the size of the nonaqueous electrolytesecondary battery 1. In a case where the nonaqueous electrolytesecondary battery 1 is a coin type for back-up which is dedicated tovarious electronic apparatuses, for example, the thickness may beapproximately 300 μm to 1000 μm.

The positive electrode 10 may be manufactured by a manufacturing methodthat is known in the related art.

Examples of a method of manufacturing the positive electrode 10 includea method in which the positive electrode active material, and thepositive electrode conductive assistant and/or the positive electrodebinder, which are added as necessary, are mixed to obtain a positiveelectrode mixture, and the positive electrode mixture iscompression-molded into an arbitrary shape.

A pressure during the compression molding is determined in considerationof a kind of the positive electrode conductive assistant and the like,and for example, may be set to 0.2 ton/cm² to 5 ton/cm².

As the positive electrode current collector 14, a material that is knownin the related art may be used, and examples thereof include aconductive resin adhesive including carbon as a conductive filler, andthe like.

Negative Electrode

In the negative electrode 20, a kind of a negative electrode activematerial is not particularly limited. A negative electrode activematerial that is conventionally known in this field is used, andexamples thereof include carbon, an alloy-based negative electrode suchas Li—Al, a silicon oxide, and the like. In addition, an active materialthat is obtained by mixing an appropriate binder, polyacrylic acid as abinding agent, graphite as a conductive assistant, and the like may beused. Particularly, it is preferable that the negative electrode activematerial contain at least one of SiO, SiO₂, Si, WO₂, WO₃, and an Li—Alalloy. When the above-described material is used in the negativeelectrode 20 as the negative electrode active material, a reactionbetween the electrolytic solution 50 and the negative electrode 20 at acharging and discharging cycle is suppressed, and thus it is possible toprevent a decrease in capacity, and cycle characteristics are improved.

In addition, in the negative electrode 20, it is more preferable thatthe negative electrode active material be configured by SiO or SiO₂,that is, a silicon oxide expressed by SiO_(X) (0≤X<2). When the siliconoxide having the above-described composition is used as the negativeelectrode active material, it is possible to use the nonaqueouselectrolyte secondary battery 1 with a high voltage, and the cyclecharacteristics are improved. In addition, as the negative electrodeactive material, the negative electrode 20 may contain any one ofdifferent negative electrode active materials in addition to SiO_(X)(0≤X<2).

In a case of using the material as the negative electrode activematerial, a particle size (D50) thereof is not particularly limited, andthe particle size is preferably 0.1 μm to 30 μm, and more preferably 1μm to 10 μm. If the particle size (D50) of the negative electrode activematerial is less than the lower limit of the preferable range, when thenonaqueous electrolyte secondary battery is exposed to a hightemperature, reactivity increases, and thus handing becomes difficult.In addition, when the particle size exceeds the upper limit thereof, adischarging rate may decrease.

In addition, in this embodiment it is preferable that the negativeelectrode active material in the negative electrode 20 contain lithium(Li) and SiO_(X) (0≤X<2), and a molar ratio (Li/SiO_(X)) thereof be in arange of 3.9 to 4.9. As described above, when the negative electrodeactive material is configured by lithium (Li) and SiO_(X), and a molarratio thereof is set to the above-described range, it is possible toobtain an effect capable of preventing charging abnormality and thelike. In addition, even when the nonaqueous electrolyte secondarybattery 1 is used or stored for a long period of time under ahigh-temperature environment, it is possible to obtain an effect ofimproving storage characteristics without a decrease in dischargingcapacity.

When the molar ratio (Li/SiO_(X)) is less than 3.9, Li is deficient, andthus Li deficiency occurs after use or storage for a long period of timeunder a high-temperature environment, and thus discharging capacitydecreases.

On the other hand, when the molar ratio (Li/SiO_(X)) exceeds 4.9, Li isexcessive, and thus charging abnormality may occur. In addition, metalLi remains without being trapped in SiO_(X), and thus resistanceincreases and discharging capacity may decrease.

In addition, in this embodiment, it is more preferable that the molarratio (Li/SiO_(X)) in the above-described range be set by selecting amore appropriate range in accordance with a kind of the positiveelectrode active material contained in the above-described positiveelectrode 10. For example, in a case of using lithium titanate as thepositive electrode active material, it is more preferable that the molarratio (Li/SiO_(X)) in the negative electrode active material be set to arange of 4.0 to 4.7. In addition, in a case of using lithium manganeseoxide as the positive electrode active material, as described above, themolar ratio (Li/SiO_(X)) in the negative electrode active material isset to a range of 3.9 to 4.9. As described above, when the molar ratio(Li/SiO_(X)) of the negative electrode active material is set to a rangein accordance with the kind of the positive electrode active material,it is possible to obtain an effect of suppressing an increase in initialresistance and of preventing charging abnormality and the like, or it ispossible to more significantly obtain an effect of improving storagecharacteristics without a decrease in discharging capacity even afteruse or storage for a long period of time under a high-temperatureenvironment.

An amount of the negative electrode active material in the negativeelectrode 20 is determined in consideration of discharging capacity andthe like that are demanded for the nonaqueous electrolyte secondarybattery 1, and the amount is preferably equal to or more than 50 mass %,and more preferably 60 mass % to 80 mass %.

In the negative electrode 20, when the amount of the negative electrodeactive material configured by the above-described material is equal toor more than the lower limit of the preferable range, it is easy toobtain sufficient discharging capacity. In addition, the amount of thenegative electrode active material is equal to or less than the upperlimit thereof, it is easy to mold the negative electrode 20.

The negative electrode 20 may contain a conductive assistant(hereinafter, the conductive assistant that is used in the negativeelectrode 20 may be referred to as a “negative electrode conductiveassistant”). The negative electrode conductive assistant is the same asthe positive electrode conductive assistant.

The negative electrode 20 may contain a binder (hereinafter, the binderthat is used in the negative electrode 20 may be referred to as a“negative electrode binder”).

Examples of the negative electrode binder include polyvinylidenefluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PA),carboxymethyl cellulose (CMC), polyimide (PI), polyamide imide (PAI),and the like. Among these, the polyacrylic acid is preferable, and across-linking type polyacrylic acid is more preferable.

In addition, as the negative electrode binder, the above-describedmaterials may be used alone or in combination of two or more kindsthereof. In addition, in a case of using the polyacrylic acid as thenegative electrode binder, it is preferable that the polyacrylic acid beadjusted in advance to pH 3 to pH 10. For the pH adjustment in thiscase, for example, an alkali metal hydroxide such as lithium hydroxide,or an alkali-earth metal hydroxide such as magnesium hydroxide may beused.

An amount of the negative electrode binder in the negative electrode 20may be set, for example, to 1 mass % to 20 mass %.

In addition, the size and the thickness of the negative electrode 20 arethe same as the size and the thickness of the positive electrode 10.

In addition, the nonaqueous electrolyte secondary battery 1 illustratedin FIG. 1 employs a configuration in which the lithium foil 60 isprovided on a surface of the negative electrode 20, that is, between thenegative electrode 20 and the separator 30 to be described later.

As a method of manufacturing the negative electrode 20, it is possibleto employ a method in which the above-described material is used as thenegative electrode active material, and the negative electrodeconductive assistant and/or the negative electrode binder are mixed asnecessary to prepare a negative electrode mixture, and the negativeelectrode mixture is compression-molded into an arbitrary shape.

A pressure during the compression molding is determined in considerationof a kind of the negative electrode conductive assistant and the like,and for example, may be set to 0.2 ton/cm² to 5 ton/cm².

In addition, the negative electrode current collector 24 may beconfigured by using the same material as that of the positive electrodecurrent collector 14.

Separator

The separator 30 is interposed between the positive electrode 10 and thenegative electrode 20, and as the separator 30, an insulating film,which has large ion permeability, is excellent in heat resistance, andhas a predetermined mechanical strength, is used.

As the separator 30, a separator formed from a material, which is usedin a separator of a nonaqueous electrode secondary battery in therelated art and satisfies the above-described characteristics, may beapplied without any limitation. Examples of the material include glasssuch as alkali glass, borosilicate glass, quartz glass, and lead glass,non-woven fabric or fiber configured by a resin such as polyphenylenesulfide (PPS), polyether ether ketone (PEEK), polyethylene terephthalate(PET), polyamide-imide (PAI), polyamide, polyimide (PI), aramid,cellulose, a fluorine resin, and ceramics, and the like. Among these, asthe separator 30, it is more preferable to use the non-woven fabricconfigured by glass fiber. The glass fiber is excellent in mechanicalstrength and has large ion permeability, and thus the glass fiberreduces internal resistance. Accordingly, it is possible to improvedischarging capacity.

The thickness of the separator 30 is determined in consideration of thesize of the nonaqueous electrolyte secondary battery 1, a material ofthe separator 30, and the like, and for example, may be set toapproximately 5 μm to 300 μm.

Capacity Balance Between Negative Electrode and Positive Electrode

In the nonaqueous electrolyte secondary battery 1 of this embodiment, itis preferable that capacity balance (negative electrode capacity(mAh)/positive electrode capacity (mAh)), which is expressed by capacityof the negative electrode 20 and capacity of the positive electrode 10,be in a range of 1.56 to 2.51.

When the capacity balance between the negative electrode 20 and thepositive electrode 10 is set to the above-described range, apredetermined margin can be secured to the negative electrode sidecapacity. Accordingly, for example, even when decomposition of thenegative electrode active material rapidly progresses due to a batteryreaction, it is possible to secure the negative electrode capacity thatis equal to or more than a constant value. Accordingly, even when thenonaqueous electrolyte secondary battery 1 is used and stored for a longperiod of time under a strict high-temperature and high-humidityenvironment, a decrease in discharging capacity is suppressed, and thusit is possible to obtain an effect of improving storage characteristics.

When the capacity balance between the negative electrode 20 and thepositive electrode 10 is less than 1.56, deterioration increases duringuse for a long period of time under a high-temperature environment, andthus capacity retention becomes difficult. On the other hand, when thecapacity balance between the negative electrode 20 and the positiveelectrode 10 exceeds 2.51, it is difficult to obtain sufficientdischarging capacity.

In the nonaqueous electrolyte secondary battery 1 of this embodiment,after the caulking tip end 12 b of the positive electrode casing 12 isdisposed in an inward direction than the tip end 22 a of the negativeelectrode casing 22, and the size of the nonaqueous electrolytesecondary battery 1, the radius of curvature R of the side surfaceportion 12 d of the positive electrode casing 12, and the sizerelationship between the nonaqueous electrolyte secondary battery 1 andthe positive electrode casing 12 are respectively defined as describedabove, the capacity balance between the negative electrode 20 and thepositive electrode 10 is configured to the above-described range, andthus even in a case of use or storage for a long period of time under ahigh-temperature environment, it is possible to retain high dischargingcapacity and storage characteristics become excellent.

Use of Nonaqueous Electrolyte Secondary Battery

As described above, the nonaqueous electrolyte secondary battery 1 ofthis embodiment has high sealing properties, and even in a case of useor storage for a long period of time under a high-temperatureenvironment, high discharging capacity can be retained, sufficientdischarging capacity can be obtained in a broad temperature range, andstorage characteristics are excellent. Accordingly, the nonaqueouselectrolyte secondary battery 1 is appropriately used as a back-up powersupply with a voltage value of, for example, 2 V to 3 V.

Operational Effect

As described above, according to the nonaqueous electrolyte secondarybattery 1 that is an embodiment of the invention, as described above,when the caulking tip end 12 b in the opening 12 a of the positiveelectrode casing 12 is disposed in an inward direction the tip end 22 aof the negative electrode casing 22, and the size of the nonaqueouselectrolyte secondary battery 1, the radius of curvature R of the sidesurface portion 12 d of the positive electrode casing 12, and the sizerelationship between the nonaqueous electrolyte secondary battery 1 andthe positive electrode casing 12 are respectively set in theabove-described ranges, it is possible to reliably press the negativeelectrode casing 22 by the positive electrode casing 12, and it ispossible to compress the gasket 40 at a sufficient compression ratio,and thus sealing conditions are defined in an appropriate range.

According to this, even when the nonaqueous electrolyte secondarybattery 1 having a size in which the diameter d is in 6.6 mm to 7.0 mm,and the height h1 is 1.9 mm to 2.3 mm is used or stored under ahigh-temperature environment, occurrence of a gap between the positiveelectrode casing 12 or the negative electrode casing 22 and the gasket40 is suppressed and thus sealing properties of the battery can beimproved, and thus volatilization of the electrolytic solution orintrusion of moisture in the air into the inside of the battery can beeffectively prevented.

Accordingly, it is possible to provide the nonaqueous electrolytesecondary battery 1 in which even under a high-temperature environment,battery characteristics do not deteriorate, sufficient dischargingcapacity can be retained, discharging capacity is large, and excellentstorage characteristics are provided.

EXAMPLES

Next, the invention will be described in more detail with reference toExamples and Comparative Examples. However, a range of the invention isnot limited by Examples. The nonaqueous electrolyte secondary batteryrelated to the invention may be embedded by making appropriatemodifications in a range not departing from the gist of the invention.

Examples 1 to 4

In Example 1, as the nonaqueous electrolyte secondary battery, thecoin-type nonaqueous electrolyte secondary battery illustrated in FIG. 1was prepared. In addition, in these examples, lithium titanate(Li₄Ti₅O₁₂) was used as the positive electrode active material, and SiOwas used as the negative electrode active material. A nonaqueouselectrolyte secondary battery (lithium secondary battery) of a coin-type(621 size) having an outer diameter (diameter d) of 6.8 mm and athickness (height h1) of 2.1 mm in a cross-sectional view illustrated inFIG. 1 was prepared, and sealing properties under a high-temperature andhigh-humidity environment were evaluated.

Preparation of Battery

With regard to the positive electrode 10, first, graphite as aconductive assistant and polyacrylic acid as a binding agent were mixedto commercially available lithium titanate (Li₄Ti₅O₁₂) in a ratio oflithium titanate:graphite:polyacrylic acid=90:8:2 (a mass ratio) toprepare a positive electrode mixture.

Subsequently, 18 mg of the positive electrode mixture that was obtainedwas compression-molded with a compression pressure of 2 ton/cm² toobtain a disk-shaped pellet having a diameter of 3.7 mm.

Next, the pellet (positive electrode 10) that was obtained was bonded toan inner surface of the positive electrode casing 12 formed fromstainless steel (NAS64: average plate thickness t=0.20 mm) using aconductive resin adhesive containing carbon to integrate the pellet andthe positive electrode casing 12, thereby obtaining a positive electrodeunit. Then, the positive electrode unit was decompressed, heated, anddried at 120° C. for 11 hours in the air.

In addition, a sealing agent was applied to an inner side surface of theopening 12 a of the positive electrode casing 12 in the positiveelectrode unit.

Next, with regard to the negative electrode 20, first, a materialobtained by pulverizing commercially available SiO was prepared as thenegative electrode active material, and graphite as a conductive agentand polyacrylic acid as a binding agent were mixed to the negativeelectrode active material in a ratio of 54:44:2 (mass ratio) to preparea negative electrode mixture.

Subsequently, 6.4 mg of the negative electrode mixture that was obtainedwas compression-molded with a compression pressure of 2 ton/cm² toobtain a disk-shaped pellet having a diameter of 3.8 mm.

Next, the pellet (negative electrode 20) that was obtained was bonded toan inner surface of the negative electrode casing 22 formed fromstainless steel (SUS304-BA: t=0.20 mm) using a conductive resin adhesivecontaining carbon as a conductive filler to integrate the pellet and thenegative electrode casing 22, thereby obtaining a negative electrodeunit. Then, the negative electrode unit was decompressed, heated, anddried at 160° C. for 11 hours in the air.

Furthermore, lithium foil 60 punched with a diameter of 3.6 mm and athickness of 0.42 mm was compressed onto the negative electrode 20having a pellet shape to prepare a lithium-negative electrode stackedelectrode.

As described above, in these examples, nonaqueous electrolyte secondarybatteries were prepared with a configuration in which the positiveelectrode current collector 14 and the negative electrode currentcollector 24, which are illustrated in FIG. 1, were not provided, thepositive electrode casing 12 was allowed to have a function of thepositive electrode current collector, and the negative electrode casing22 was allowed to have a function of the negative electrode currentcollector.

Next, non-woven fabric configured by glass fiber was dried, and waspunched into a disk shape having a diameter of 4.9 mm, thereby preparingthe separator 30. Then, the separator 30 was placed on the lithium foil60 that was compressed onto the negative electrode 20, and the gasket 40formed from polypropylene was disposed at the opening of the negativeelectrode casing 22.

Next, an organic solvent was adjusted in accordance with the followingmixing ratio (volume %), and a supporting salt was dissolved in theorganic solvent to adjust the electrolytic solution. At this time, asthe organic solvent, a mixed solvent was adjusted by mixing propylenecarbonate (PC), ethylene carbonate (EC), and dimethoxy ethane (DME) in aratio of (PC:EC:DME)=(1:1:2) in terms of a volume ratio. Next, as thesupporting salt, Li(CF₃SO₂)₂N was dissolved in the mixed solvent, whichwas obtained, in a concentration of 1 mol/L, thereby obtaining theelectrolytic solution 50.

In addition, the electrolytic solution 50, which was adjusted in theabove-described procedure, filled the positive electrode casing 12 andthe negative electrode casing 22 in a total amount of 15 μL per onebattery.

Next, the negative electrode unit was caulked to the positive electrodeunit in order for the separator 30 to come into contact with thepositive electrode 10. At this time, caulking was performed in such amanner that the caulking tip end 12 b in the opening 12 a of thepositive electrode casing 12 was disposed in an inward direction of thenegative electrode casing 22 than the tip end 22 a of the negativeelectrode casing 22, and the side surface portion 12 d of the positiveelectrode casing 12 had a curved surface shape on an opening 12 a side.At this time, processing was performed in such a manner that the radiusof curvature R (mm) of the side surface portion 12 d became a dimensionshown in Table 1. In addition, the processing was performed in such amanner that the height h2 of the positive electrode casing 12 withrespect to the height h1 of the nonaqueous electrolyte secondary battery1 became a ratio (h2/h1) shown in the following Table 1. In addition, asshown in the following Table 1, the radius of curvature R (mm) of theside surface portion 12 d of the positive electrode casing 12 was set to1.0 mm in Examples 1 to 4.

In addition, the opening of the positive electrode casing 12 was caulkedto seal the positive electrode casing 12 and the negative electrodecasing 22, and then the resultant object was left as is at 25° C. forseven days to prepare nonaqueous electrode secondary batteries ofExamples 1 to 4.

High-Temperature and High-Humidity Storage Test: Evaluation of SealingProperties

With respect to the nonaqueous electrolyte secondary batteries ofExamples 1 to 4 which were obtained in the above-described procedure,the following high-temperature and high-humidity storage test (HHTS) wasperformed to evaluate sealing properties (storage characteristics) undera high-temperature and high-humidity environment.

Specifically, first, each of the nonaqueous electrolyte secondarybatteries, which were obtained, was discharged with a constant currentof 5 μA (discharging current) under an environment of 25° C. until avoltage reached 1.5 V. Subsequently, a voltage of 2.3 V was applied for48 hours under an environment of 25° C. Then, capacity when thenonaqueous electrolyte secondary battery was discharged with a constantcurrent of 5 μA (discharging current) under an environment of 25° C.until a voltage reached 1.5 V was measured. The measured value is shownas initial capacity (mAh) in the following Table 1. In addition, withregard to internal resistance (Ω) of the nonaqueous electrolytesecondary battery that was obtained, an LCR meter was used, andimpedance at AC 1 kHz was measured to measure the internal resistancebetween the positive electrode and the negative electrode. The measuredvalue is shown in the following Table 1 as initial resistance (Ω).

Next, the nonaqueous electrolyte secondary battery was left as is for 30days while being exposed to a high-temperature and high-humidityenvironment of 80° C. and 90% RH by using a high-humidity andconstant-temperature tester (HHTS).

In addition, with respect to the nonaqueous electrolyte secondarybattery exposed to the high-temperature and high-humidity environment ofthe above-described conditions, capacity when the nonaqueous electrolytesecondary battery was discharged with a constant current of 5 μA(discharging current) under an environment of 25° C. until a voltagereached 1.0 V was measured. The measured value is shown as capacity(mAh) after a test (after storage for 30 days) in the following Table 1.In addition, the internal resistance between the positive electrode andthe negative electrode of the nonaqueous electrolyte secondary batterythat was exposed to the high-temperature and high-humidity environmentof the above-described conditions was measured by the above-describedmethod. The measured value is shown as resistance (Ω) after a test(after storage for 30 days) in the following Table 1.

In the high-temperature and high-humidity storage test in theseexamples, particularly, a variation (reduced state) in capacity afterthe test with respect to the initial capacity was set as an index of thestorage characteristics, that is, the sealing properties of the batteryunder a high-temperature environment.

TABLE 1 Dimensions of positive Internal Discharging electrode casing(mm) resistance (Ω) capacity (mAh) R of side After After Capacitysurface h2/h1 storage for storage for retention portion Height h2 (%)Initial 30 days Initial 30 days ratio Example 1 1.0 1.44 68.6 43.8 86.32.63 2.32 88.0% Example 2 1.0 1.47 70.0 41.8 81.1 2.60 2.45 94.3%Example 3 1.0 1.51 71.9 45.9 90.0 2.60 2.53 97.2% Example 4 1.0 1.5272.4 46.9 95.0 2.57 2.31 90.0% Comparative 1.0 1.54 73.3 42.9 105.1 2.612.25 86.0% Example 1

Comparative Example 1

In Comparative Example 1, a nonaqueous electrolyte secondary battery wasprepared in accordance with the same conditions and the same procedureas in Example 1 except that with respect to the preparation conditionsof the battery in Example 1, the caulking was performed in order for theheight h2 of the positive electrode casing 12 with respect to the heighth1 of the nonaqueous electrolyte secondary battery 1 to be a ratio(h2/h1) shown in the following Table 1, and then the sealing propertieswere evaluated under that same conditions as described above. The resultis shown in Table 1.

Examples 5 to 7 Preparation of Battery

In Examples 5 to 7, coin-type nonaqueous electrolyte secondary batteriesillustrated in FIG. 1 were prepared in accordance with the sameconditions and the same procedure as in Example 4 except that withrespect to the preparation conditions of the battery in Example 1, theradius of curvature R (mm) of the side surface portion 12 d of thepositive electrode casing 12 was changed to a dimension shown in thefollowing Table 2.

Evaluation of Internal Resistance

With respect to the nonaqueous electrolyte secondary batteries ofExamples 5 and 6 which were obtained in the above-described procedure,the following high-temperature storage test was performed to evaluate avariation in the internal resistance under a high-temperatureenvironment.

Specifically, first, the internal resistance (Ω) between the positiveelectrode and the negative electrode of the nonaqueous electrolytesecondary batteries which were obtained was measured by the same methodas described above. The measured internal resistance is shown as initialresistance (Ω) in Table 2.

Next, the nonaqueous electrolyte secondary battery was left as is for 30days while being exposed to a high-temperature and high-humidityenvironment of 80° C. and 90% RH by using a high-humidity andconstant-temperature tester (HHTS).

In addition, with respect to the nonaqueous electrolyte secondarybattery exposed to the high-temperature and high-humidity environment ofthe above-described conditions, the internal resistance between thepositive electrode and the negative electrode was measured by theabove-described method. The measured value is shown as resistance (Ω)after a test (after storage for 30 days) in the following Table 2.

In the high-humidity and constant-temperature test performed in thisexample, a variation (resistance increased state) of the resistanceafter the test with respect to the initial resistance was set as anindex of the battery characteristics under a high-temperatureenvironment.

TABLE 2 Internal resistance (Ω) R of side surface After portion ofpositive storage for Resistance electrode casing Initial 30 daysincrease rate Example 5 0.8 35.0 72.8 208% Example 6 1 36.0 90.4 251%Example 7 1.1 35.1 91.2 260% Comparative 1.2 37.8 107.5 285% Example 2

Comparative Example 2

In Comparative Example 2, a coin-type nonaqueous electrolyte secondarybattery illustrated in FIG. 1 were prepared in accordance with the sameconditions and the same procedure as in Examples 5 to 7 except that withrespect to the preparation conditions of the battery in Examples 5 to 7,the radius of curvature R (mm) of the side surface portion 12 d of thepositive electrode casing 12 was changed to a dimension shown in Table2.

In addition, with respect to the nonaqueous electrolyte secondarybatteries which were obtained, a high-temperature storage test wasperformed under the same conditions as in Examples 5 to 7 to evaluate avariation in the internal resistance under a high-temperatureenvironment.

Examples 8 to 11, and Test Example 1

In Examples 8 to 11, and Test Example 1, as the negative electrodeactive material used in the negative electrode 20, a negative electrodeactive material containing lithium (Li) and SiO was used, and a molarratio (Li/SiO) thereof was set to a ratio shown in the following Table3.

In addition, in Examples 8 to 11, and Test Example 1, the nonaqueouselectrolyte secondary battery 1 was set to a coin type (621 size) havingan outer diameter of 6.8 mm (diameter d) and a thickness of 2.1 mm(height h1) in the cross-sectional view illustrated in FIG. 1, andrespective dimensions were adjusted in such a manner that a ratiobetween a radius of curvature R (mm) of a side surface portion 12 d ofthe positive electrode casing 12, a height h2 of the positive electrodecasing 12, and a height h1 of the nonaqueous electrolyte secondarybattery 1 satisfies the range defined in the aspect of the invention.

In addition, in Examples 8 to 11, and Test Example 1, respectivecapacities were set in such a manner that the capacity balance (negativeelectrode capacity (mAh)/positive electrode capacity (mAh)) between thecapacity of the negative electrode 20 and the capacity of the positiveelectrode 10 became 1.95, and coin-type nonaqueous electrolyte secondarybatteries illustrated in FIG. 1 were prepared in a state in which otherconditions and a procedure were made to be equal to those in Example 1.

In addition, with respect to the nonaqueous electrolyte secondarybatteries of Examples 8 to 11 and Test Example 1 which were obtained inthe above-described procedure, the following high-temperature andhigh-humidity storage test (HHTS) was performed to evaluate storagecharacteristics under a high-temperature and high-humidity environment.

Specifically, first, each of the nonaqueous electrolyte secondarybatteries, which were obtained, was discharged by using resistance of 30kΩ as current limitation resistance under an environment of 25° C. untila voltage reached 1.0 V. Subsequently, a voltage of 2.3 V was appliedfor 72 hours by using constant resistance of 330Ω under an environmentof 25° C.

Then, capacity when the nonaqueous electrolyte secondary battery wasdischarged using resistance of 30 kΩ as the current limitationresistance under an environment of 25° C. until a voltage reached 1.0 Vwas measured. The measured value is shown as initial capacity (mAh) inthe following Table 3.

Next, the above-described nonaqueous electrolyte secondary battery wasleft as it is for 30 days while being exposed to a high-temperature andhigh-humidity environment of 80° C. and 90% RH by using a high-humidityand constant-temperature tester (HHTS).

In addition, with respect to the nonaqueous electrolyte secondarybattery exposed to the high-temperature and high-humidity environment ofthe above-described conditions, capacity when the nonaqueous electrolytesecondary battery was discharged by using resistance of 30 kΩ as thecurrent limitation resistance under an environment of 25° C. until avoltage reached 1.0 V was measured. The measured value is shown ascapacity (mAh) after a test (after storage for 30 days) in the followingTable 3.

In the high-temperature and high-humidity storage test in theseexamples, particularly, a variation (reduced state) in capacity afterthe test with respect to the initial capacity was set as an index of thestorage characteristics of the battery under a high-temperatureenvironment.

TABLE 3 Discharging capacity (mAh) After storage Capacity Molar ratiofor 30 days retention (Li/SiO) Initial (80° C., 90%) ratio Test 3.812.46 1.62 65.6% Example 1 Example 8 4.04 2.52 1.94 76.8% Example 9 4.272.50 1.97 78.7% Example 10 4.44 2.54 1.98 78.1% Example 11 4.63 2.502.36 94.4%

Examples 12 to 15, and Test Example 2

In Examples 12 to 15, and Test Example 2, as the negative electrodeactive material used in the negative electrode 20, a negative electrodeactive material containing lithium (Li) and SiO was used, and a molarratio (Li/SiO) thereof was set to a ratio shown in the following Table4. In addition, in Examples 11 to 14, and Test Example 2, with regard tothe positive electrode active material used in the positive electrode,lithium manganese oxide (Li₄Mn₅O₁₂) was used instead of lithium titanate(Li₄Ti₅O₁₂).

In addition, in Examples 12 to 15, and Test Example 2, respectivecapacities were set in such a manner that the capacity balance (negativeelectrode capacity (mAh)/positive electrode capacity (mAh)) between thecapacity of the negative electrode 20 and the capacity of the positiveelectrode 10 became 2.03, and coin-type nonaqueous electrolyte secondarybatteries illustrated in FIG. 1 were prepared in a state in which otherconditions and a procedure were made to be equal to those in Example 7and the like.

In addition, with respect to the nonaqueous electrolyte secondarybatteries of Examples 12 to 15, and Test Example 2 which were obtainedin the above-described procedure, the following high-temperature storagetest was performed to evaluate capacity retention ratio under ahigh-temperature environment.

Specifically, first, each of the nonaqueous electrolyte secondarybatteries, which were obtained, was constant-current-discharged by usingresistance of 47 kΩ as current limitation resistance under anenvironment of 25° C. until a voltage reached 2.0 V. Subsequently, avoltage of 3.1 V was applied for 72 hours by using constant resistanceof 330Ω under an environment of 25° C.

Then, capacity when the nonaqueous electrolyte secondary battery wasdischarged using resistance of 47 kΩ as the current limitationresistance under an environment of 25° C. until a voltage reached 2.0 Vwas measured. The measured value is shown as initial capacity (mAh) inthe following Table 4.

Next, the above-described nonaqueous electrolyte secondary battery wasleft as it is for 80 days while being exposed to a high-temperatureenvironment of 85° C. by using a high-temperature tester.

In addition, with respect to the nonaqueous electrolyte secondarybattery exposed to the high-temperature environment of theabove-described conditions, capacity when the nonaqueous electrolytesecondary battery was constant-current-discharged by using resistance of47 kΩ as the current limitation resistance under an environment of 25°C. until a voltage reached 2.0 V was measured. The measured value isshown as capacity (mAh) after a test (after 80 days) in the followingTable 4, and a capacity retention ratio is also shown in the followingTable 4.

In the high-temperature storage test in these examples, a variation(reduced state) in capacity after the test with respect to the initialcapacity was set as an index of the capacity retention ratio under ahigh-temperature environment.

TABLE 4 Discharging capacity (mAh) After storage Capacity Molar ratio at85° C. retention (Li/SiO) Initial for 80 days ratio Test 3.52 3.39 2.5575.3% Example 2 Example 12 3.96 3.48 2.67 76.9% Example 13 4.19 3.472.66 76.8% Example 14 4.36 3.43 2.67 78.0% Example 15 4.79 3.30 2.6281.8%

Evaluation Result

As shown in Table 1, in the nonaqueous electrolyte secondary batteriesof Examples 1 to 4 in which the caulking tip end 12 b in the opening 12a of the positive electrode casing 12 was disposed in an inwarddirection than the tip end 22 a of the negative electrode casing 22, andthe size of the nonaqueous electrolyte secondary battery 1, the radiusof curvature R of the side surface portion 12 d of the positiveelectrode casing 12, and the size relationship between the nonaqueouselectrolyte secondary battery 1 and the positive electrode casing 12were defined in the ranges defined in the invention (the aspect), thecapacity retention ratio after the high-temperature and high-humiditytest for 30 days was 88.0% to 97.2% and was higher in comparison toComparative Example 1 (86.0%), and thus it could be seen that thecapacity retention ratio under a high-temperature and high-humidityenvironment was excellent. In addition, in the nonaqueous electrolytesecondary batteries of Examples 1 to 4, the internal resistance (Ω)after the high-temperature and high-humidity test was 81.1Ω to 95.0Ω,and was smaller in comparison to Comparative Example 1 (105.1Ω), andthus it could be seen that the battery characteristics were excellent.In addition, as illustrated in a schematic cross-sectional view of FIG.3, in the nonaqueous electrolyte secondary battery of Example 1,satisfactory sealing properties were retained without occurrence of agap and the like at the inside of the battery even after thehigh-temperature and high-humidity test.

From these results, it is apparent that in the nonaqueous electrolytesecondary batteries of Examples 1 to 4, an inner electrolyte did notvolatilize to the outside, and moisture in the air did not intrude intothe inside of the battery, and thus satisfactory sealing properties andbattery characteristics.

In addition, as shown in Table 2, in the nonaqueous electrolytesecondary batteries of Examples 5 to 7 in which the caulking tip end 12b in the opening 12 a of the positive electrode casing 12 was disposedin an inward direction than the tip end 22 a of the negative electrodecasing 22, the size of the nonaqueous electrolyte secondary battery 1,and the size relationship between the nonaqueous electrolyte secondarybattery 1 and the positive electrode casing 12 were set similar to thosein Example 1, and the radius of curvature R of the side surface portion12 d of the positive electrode casing 12 was changed in the rangedefined in the invention (the aspect), the internal resistance (Ω) afterthe high-temperature and high-humidity test was 72.8Ω to 91.2Ω and wassmaller in comparison to Comparative Example 2 (107.5Ω). Accordingly, itis apparent that satisfactory sealing properties and batterycharacteristics are provided. In addition, as illustrated in a schematiccross-sectional view of FIG. 5, in the nonaqueous electrolyte secondarybattery of Example 5 in which the radius of curvature R of the sidesurface portion 12 d of the positive electrode casing 12 was set to 0.8mm, relatively satisfactory sealing properties were retained withoutoccurrence of a large gap and the like at the inside of the battery evenafter the high-temperature and high-humidity test. In addition, in thenonaqueous electrolyte secondary battery of Example 6 in which theradius of curvature R of the side surface portion 12 d of the positiveelectrode casing 12 was set to 1.0 mm, and the nonaqueous electrolytesecondary battery of Example 7 in which the radius of curvature R of theside surface portion 12 d of the positive electrode casing 12 was set to1.1 mm, as is the case with Example 5 illustrated in a schematiccross-sectional view of FIG. 5, very satisfactory sealing propertieswere retained without occurrence of a gap and the like at the inside ofthe battery even after the high-temperature and high-humidity test.

On the other hand, in Comparative Example 1 as shown in Table 1, thecapacity retention ratio after the high-temperature and high-humiditytest for 30 days was 86.0% and was lower in comparison to Examples 1 to4. In addition, In addition, as illustrated in a schematiccross-sectional view of FIG. 4, in the nonaqueous electrolyte secondarybattery of Comparative Example 1, a gap occurred between the positiveelectrode casing and the gasket after the high-temperature andhigh-humidity test, and thus it can be seen that the sealing propertiesdeteriorate.

From these results, in Comparative Example 1, among the conditionsdefined in the invention (the aspect), the ratio (h2/h1) of the heighth2 of the positive electrode casing 12 to the height h1 of thenonaqueous electrolyte secondary battery 1 deviated from the definedrange. Accordingly, it is apparent that a gap and the like occurredbetween the positive electrode casing and the gasket (or between thenegative electrode casing and the gasket), and the electrolyte solutionvolatilized to the outside or moisture in the air intruded into theinside of the battery, and thus discharging capacity decreased.

In addition, in Comparative Example 2 as shown in Table 2, the internalresistance (Ω) after the high-temperature and the high-humidity test was107.5Ω, and was larger in comparison to Examples 5 to 7. In thenonaqueous electrolyte secondary battery of Comparative Example 2, asillustrated in a schematic cross-sectional view of FIG. 5, as is thecase with Example 1, Example 5, and the like, a gap and the like did notoccur after the high-temperature and high-humidity test, particularly,at the inside of the battery. However, in Comparative Example 2, theradius of curvature R (mm) of the side surface portion of the positiveelectrode casing exceeded the range defined in the invention (theaspect), and thus it is considered that the height h2 of the positiveelectrode casing tends to vary, and this tendency has led to an increasein the internal resistance.

In addition, as shown in Table 3 and Table 4, in Examples 8 to 15 inwhich the sealing conditions between the positive electrode casing 12and the negative electrode casing 22 were set in the range defined inthe invention (the aspect), an active material containing lithium (Li)and SiO was used as the negative electrode active material used in thenegative electrode 20, and a molar ratio (Li/SiO) thereof was limited toan appropriate range (3.9 to 4.9), the capacity retention ratio afterthe high-temperature and high-humidity storage test is 76.8% to 94.4%,the capacity retention ratio after the high-temperature storage test is76.8% to 81.8%, and these capacity retention ratios are higher incomparison to Test Example 1 or Test Example 2 in which an amount of Liwas smaller, and thus it can be seen that the capacity retention ratioin an high-temperature and high-humidity environment and in ahigh-temperature environment is excellent.

Here, as shown in Table 3, for example, in a case of using lithiumtitanate as the positive electrode active material in the positiveelectrode 10, when the molar ratio (Li/SiO_(X)) between Li and SiO_(X)in the negative electrode active material is set to a range of 4.0 to4.7, it can be seen that an excellent capacity retention ratio can beobtained even under a high-temperature and high-humidity environment.

In addition, as shown in Table 4, in a case of using lithium manganeseoxide as the positive electrode active material in the positiveelectrode 10, when the molar ratio (Li/SiO_(X)) between Li and SiO_(X)in the negative electrode active material is in a range of 3.9 to 4.9 asdescribed above, it can be seen that an excellent capacity retentionratio can be obtained even under a high-temperature environment.

From the results of Examples described above, when the nonaqueouselectrolyte secondary battery, in which the diameter d is in a range of6.6 mm to 7.0 mm and the height h1 is in a range of 1.9 mm to 2.3 mm, isconfigured under the conditions defined in the invention, it is possibleto improve sealing properties of a battery, and it is possible toeffectively prevent occurrence of volatilization of the electrolyticsolution or intrusion of moisture in the air into the inside of thebattery under a high-temperature environment, and thus it is apparentthat the battery characteristics do not deteriorate, the dischargingcapacity is large, and excellent storage characteristics can beobtained.

According to the nonaqueous electrolyte secondary battery of theinvention, when the above-described configurations are employed, even ina case of use or storage under a high-temperature environment, thebattery characteristics do not deteriorate, the discharging capacity islarge, and excellent storage characteristics can be obtained.Accordingly, when the invention is applied, for example, to a nonaqueouselectrolyte secondary battery that is used in a field of variouselectronic apparatuses, it is also possible to contribute to animprovement in performance of various apparatuses.

What is claimed is:
 1. A nonaqueous electrolyte secondary battery,comprising: a bottomed cylindrical positive electrode casing; and anegative electrode casing fixed to an opening of the positive electrodecasing through a gasket, such that an accommodation space is definedbetween the positive electrode casing and the negative electrode casing,wherein the opening of the positive electrode casing is sealed to thenegative electrode casing side by a caulking material of the gasket toseal the accommodation space, where the caulking material has a uniformcompression ratio of at least 50%, and where a caulking tip end of thepositive electrode casing in the opening is inward of a tip end of thenegative electrode casing, and a diameter d of the nonaqueouselectrolyte secondary battery is in a range of 6.6 mm to 7.0 mm, aheight h1 of the nonaqueous electrolyte secondary battery is in a rangeof 1.9 mm to 2.3 mm, at least a part of a side surface portion of thepositive electrode casing on an opening side has a curved surface, aradius of curvature R of the curved surface is in a range of 0.8 mm to1.1 mm, and a height h2 of the positive electrode casing is in a rangeof 65% to 73% with respect to the height h1 of the nonaqueouselectrolyte secondary battery.
 2. The nonaqueous electrolyte secondarybattery according to claim 1, wherein the gasket comprises one of apolypropylene resin, polyphenylene sulfide (PPS), or a polyether etherketone (PEEK) resin.
 3. The nonaqueous electrolyte secondary batteryaccording to claim 1, wherein a positive electrode on the positiveelectrode casing side includes a lithium compound as a positiveelectrode active material, a negative electrode on the negativeelectrode casing side includes SiO_(X) (0≤X<2) as a negative electrodeactive material, a separator between the positive electrode and thenegative electrode, and an electrolytic solution that fills theaccommodation space includes at least an organic solvent and asupporting salt in the accommodation space.
 4. The nonaqueouselectrolyte secondary battery according to claim 3, wherein the positiveelectrode active material includes a lithium manganese oxide or alithium titanate.
 5. The nonaqueous electrolyte secondary batteryaccording to claim 3, wherein the negative electrode active materialincludes lithium (Li) and SiO_(X) (0≤X<2), and a molar ratio(Li/SiO_(X)) between lithium and SiO_(X) is in a range of 3.9 to 4.9. 6.The nonaqueous electrolyte secondary battery according to claim 3,wherein in the electrolytic solution, the organic solvent is a mixedsolvent that contains propylene carbonate (PC) that is a cycliccarbonate solvent, ethylene carbonate (EC) that is a cyclic carbonatesolvent, and dimethoxy ethane (DME) that is a chain ether solvent. 7.The nonaqueous electrolyte secondary battery according to claim 6,wherein in the organic solvent, a mixing ratio between the propylenecarbonate (PC), the ethylene carbonate (EC), and the dimethoxy ethane(DME) is (PC:EC:DME)=0.5 to 1.5:0.5 to 1.5:1 to 3 by a volume ratio. 8.The nonaqueous electrolyte secondary battery according to claim 3,wherein in the electrolytic solution, the supporting salt is lithiumbis(trifluoromethane) sulfonimide (Li(CF₃SO₂)₂N).
 9. The nonaqueouselectrolyte secondary battery according to claim 3, wherein theseparator comprises a glass fiber.
 10. A nonaqueous electrolytesecondary battery, comprising: a bottomed cylindrical positive electrodecasing; and a negative electrode casing fixed to an opening of thepositive electrode casing through a gasket, such that an accommodationspace is defined between the positive electrode casing and the negativeelectrode casing, wherein the opening of the positive electrode casingis sealed to the negative electrode casing side by a caulking materialof the gasket to seal the accommodation space, a caulking tip end of thepositive electrode casing in the opening is inward of a tip end of thenegative electrode casing, and a diameter d of the nonaqueouselectrolyte secondary battery is in a range of 6.6 mm to 7.0 mm, aheight h1 of the nonaqueous electrolyte secondary battery is in a rangeof 1.9 mm to 2.3 mm, at least a part of a side surface portion of thepositive electrode casing on an opening side has a curved surface, aradius of curvature R of the curved surface is in a range of 0.8 mm to1.1 mm, and a height h2 of the positive electrode casing is in a rangeof 65% to 73% with respect to the height h1 of the nonaqueouselectrolyte secondary battery, wherein a capacity balance (negativeelectrode capacity (mAh)/positive electrode capacity (mAh)), defined asa capacity of the negative electrode and capacity of the positiveelectrode, is in a range of 1.43 to 2.51.